The use of endoscopes for diagnostic and therapeutic indications is rapidly expanding. To improve performance, endoscopes have been optimized to best accomplish their purpose. Therefore, there are upper endoscopes for examination of the esophagus, stomach and duodenum, colonoscopes for examining the colon, angioscopes for examining blood vessels, bronchoscopes for examining the bronchi, laparoscopes for examining the peritoneal cavity, and arthroscopes for examining joint spaces. The discussion which follows will apply to all of these types of endoscopes. Instruments to examine the rectum and sigmoid colon, known as flexible sigmoidoscopes, are good examples of the usefulness of this technology. These devices are expensive, used in a contaminated environment for a procedure which is brief (5-10 minutes) and where problems of cleaning time and contamination are important factors. There has been a large increase in the use of the "flexible sigmoidoscope" for use in screening symptomatic and asymptomatic patients for colon and rectal cancer. Ideally, flexible sigmoidoscopes must be used rapidly and inexpensively in order to maintain the cost of such screening at acceptable levels. Typically, a clinic would like to perform five to ten sigmoidoscope examinations each hour. One significant problem with making such examinations quick and inexpensive is the time necessary for adequately cleaning the device.
Although endoscopes can be cleaned in about two to four minutes, this relatively cursory cleaning may not be adequate for complete disinfection or sterilization. Even a more complete cleaning requiring on the order of eight to ten minutes may not allow adequate cleaning, particularly in view of the increasing problems with contagious viruses. Even with the use of chemicals such as glutaraldehyde, adequate cleanliness may not be possible.
While the external surfaces of endoscopes can often be adequately cleaned, endoscopes typically have air, water, biopsy and suction channels extending along their lengths which come into contact with body tissues or fluids. It is extremely difficult to adequately clean these channels even when skilled health practitioners spend a great deal of time on the cleaning procedure.
Even if endoscopes can be adequately cleaned in eight to ten minutes, the cleaning still prevents endoscopy examinations from being relatively inexpensive. While a physician may spend five to ten minutes performing the endoscopy, he or she will generally waste a great deal of time waiting for the endoscope to be cleaned before he or she can conduct another endoscopy. A partial solution to the "idle time" problem is to purchase multiple instruments so one can be used as the others are being cleaned. However, the expense of having duplicate endoscopes of each type makes this solution impractical especially for physicians' offices and smaller clinics.
Not only must the idle time of the physician be added to the cost of endoscopic examinations, but the time spent by a nurse or other hospital personnel in the cleaning as well as the cost of disinfecting chemicals must also be added to the cost of the examination. Although washing machines are available to clean endoscopes, these machines are expensive and not significantly faster than washing by hand. As a result, with conventional endoscopic procedures, both the physician and the relatively expensive endoscope have a downtime approaching fifty percent.
Another problem with cleaning endoscopes by hand or with a washing machine is that the chemicals used are toxic and potentially injurious to the staff who use them, and the environment into which they are discharged. To use some of these chemicals safely, such as glutaraldehyde, requires a dedicated ventilated hood, which uses up space and is expensive to install and operate. The chemicals are also potentially toxic to the patient in that if residue remains after cleaning and rinsing the instrument, the patient could have a reaction to the chemicals. A limitation to this approach is that some types of chemicals may damage the outer surfaces of endoscopes after a number of washings.
In short, conventional endoscope cleaning techniques greatly increase the cost of endoscopic procedures. Furthermore, while the risk of contamination using endoscopes is often far less than the risk of alternative procedures, such as surgery, there is nevertheless a risk that endoscopes are not adequately cleaned to prevent the risk of transmission of infectious diseases from one patient to the next.
In the health care field, the problems of contaminated instruments transmitting disease from one patient to the next have generally been solved by making such instruments disposable. However, this has not been thought possible in the field of endoscopy because endoscopes are very sophisticated, and hence, expensive instruments. Moreover, it has not been thought possible to isolate the endoscope from the patient or the external environment because the endoscope itself has channels inside it that are used as a conduit for body fluids and tissues, such as, for example, in taking biopsies. The only method currently available to actually sterilize an endoscope is to use gas sterilization with ethylene oxide (ETO) gas. However, there are several significant disadvantages in using this procedure. The procedure is very slow; it takes 24 hours, during which the endoscope cannot be used. Also, the gas affects the plastic of the endoscope and may limit the life span of the instrument. The gas is toxic, and, therefore, great care must be taken to ensure that no residue remains that might cause patient irritation during contact with the endoscope. Finally, if the instrument is not thoroughly cleaned of all tissue, mucous, blood and stool, a biofilm is formed which is impenetrable, and easily killed microbes have been cultured from such endoscopes after ETO "sterilization."
U.S. Pat. No. 4,646,722, which is incorporated by reference herein, teaches the use of a disposable elastomeric sheath which is installed by inflation. The inside diameter of the sheath is undersized to the outside diameter of the endoscope such that the sheath fits the endoscope snugly upon deflation. One of the problems encountered with this approach is the possibility of over inflation of the sheath. U.S. Pat. No. 4,907,395 describes the use of an elongated bag to package the sheath and also prevent such overexpansion by acting as a restraint; the sheath expands until it contacts the wall of the bag. U.S. Pat. No. 4,991,564 addresses the issue of over inflation of the elastomeric sheath by incorporating a pressure relief valve in the inflation means. Such an approach overcomplicates the installation or removal of the sheath, especially since higher pressures may be initially required when beginning to inflate the sheath. Additionally, there may be times when the user desires to adjust the sheath, such as if the distal window of the sheath is not properly aligned with the viewing optics of the endoscope. Under these circumstances, it would be inconvenient to have to replace the sheathed endoscope back into the bag to make such adjustment. Another problem with the use of an elastomeric sheath, such as latex, is that longitudinal as well as radial expansion occurs upon inflation, and this can leave a loose, "baggy" distal end as the sheath deflates at the proximal end first. This is a problem as a tight fit is desirable for the entire length of the endoscope for manipulation. U.S. Pat. No. 4,991,564 addresses this problem by the use of a tapered sheath cover to reduce the chance of the sheath bunching up at the distal end during installation. Still another problem with the use of elastomer materials is the possibility of pinholes and tears resulting in a compromise of the barrier properties of the sheath.
The need to inflate the sheath so that it expands to contact the wall of the elongated bag, as taught in U.S. Pat. No. 4,907,395, requires a good seal at the proximal end of the sheath where the endoscope enters. U.S. Pat. No. 4,991,565 addresses this problem by use of a gasket-type seal that is free to move radially, thus allowing complete sealing around the endoscope as it is bent and moves during installation. One of the problems with this approach is pressure build-up within the sheath as the endoscope is advanced towards the distal end of the sheath, further compressing the gas. Such increased pressure will cause resistance as the endoscope is advanced, and may prevent proper seating of the distal window of the sheath against the endoscope optics. In this regard, it is important for the proximal seal between the endoscope and sheath to leak in a controlled manner so as to prevent this pressure build-up.
The placement of a tightly fitting sheath onto an endoscope can detrimentally restrict the movement and flexibility of the endoscope. Traditional endoscopes have an insertion tube constructed of a vinyl or urethane covered spring to which is coupled the articulating section comprised of metal vertebrae loosely covered with a rubber material. Such a construction gives the required axial and torsional rigidity for most of the length of the endoscope along with a more flexible articulating section which can be moved with little applied force in a relatively tight bending radius. The placement of a tight fitting sheath surrounding the endoscope, although it is needed for the length of the insertion tube, can result in poor mobility at the articulating section.
One might consider the use of a loose bag as a sheath material since one would not have to inflate it for installation, and it would not restrict the movement of the tubes contained within. Ersek in U.S. Pat. Nos. 3,794,091 and 3,809,072 describes such a design. While this would allow the tubes to more freely move during articulation of the endoscope, the bagginess of such a sheath would create discomfort for the patient during insertion of the endoscope, and it would not allow the physician to grip the endoscope tube with sufficient purchase during manipulation.